Bellaria-Igea Marina is essentially a summer town, and the experience of visiting changes dramatically depending on the month.
June to August is peak season: the beach is full, every stabilimento is open, restaurants are busy in the evenings, and the promenade fills with people from early afternoon until well after midnight. The Anteprima film festival runs in summer, usually in June, and smaller events and concerts appear throughout July and August. The downside is crowds — the beach is managed and never overwhelming, but the town is unmistakably in full resort mode. July and August are also hot, with temperatures regularly above 30°C and high humidity from the Adriatic.
May and September offer the same pleasant weather with a fraction of the crowds. The sea is warm enough to swim from late May, and in September it holds the heat of the summer. Beach clubs are open but not packed, restaurants have space, and the town feels more like itself — more Italian, less resort. These are the best months to visit if you want the Adriatic without the full summer machinery.
October to April the town largely closes. Many hotels, restaurants, and beach clubs shut for the winter, and the promenade is quiet. There is little reason to visit unless you are passing through or based in the area; the Adriatic in winter is grey and cold.